Communication related to network slice information

ABSTRACT

A base station (1) controls state transitions of a radio terminal (2) among first to third RRC states. In addition, the base station (1) explicitly or implicitly informs the radio terminal (2) about whether a network slice configured in the radio terminal (2) for data communication at least in the first RRC state is available in each cell included in a RAN notification area configured by a RAN (3). It is thus, for example, possible to allow a radio terminal in a first state (e.g., RRC_INACTIVE state) to be easily aware of the availability of network slices in a cell to be reselected or a reselected cell.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. patent application Ser. No. 16/475,764filed Jul. 3, 2019, which claims priority from International ApplicationNo. PCT/JP2017/041829 filed Nov. 21, 2017, claiming priority based onJapanese Patent Application No. 2017-000800 filed Jan. 5, 2017, thedisclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present disclosure relates to a radio communication system and, inparticular, to mobility of a radio terminal.

BACKGROUND ART

The 3rd Generation Partnership Project (3GPP) has started in 2016 thestandardization for the fifth generation mobile communication system(5G), i.e., 3GPP Release 14, to make it a commercial reality in 2020 orlater. 5G is expected to be realized by continuous enhancement/evolutionof LTE and LTE-Advanced and an innovative enhancement/evolution by anintroduction of a new 5G air interface (i.e., a new Radio AccessTechnology (RAT)). The new RAT supports, for example, frequency bandshigher than the frequency bands (e.g., 6 GHz or lower) supported byLTE/LTE-Advanced and its continuous evolution. For example, the new RATsupports centimeter-wave bands (10 GHz or higher) and millimeter-wavebands (30 GHz or higher).

In this specification, the fifth generation mobile communication systemis referred to as a 5G System or a Next Generation (NextGen) System (NGSystem). The new RAT for the 5G System is referred to as a New Radio(NR), a 5G RAT, or a NG RAT. A new Radio Access Network (RAN) for the 5GSystem is referred to as a 5G-RAN or a NextGen RAN (NG RAN). A new basestation in the NG-RAN is referred to as a NR NodeB (NR NB) or a gNodeB(gNB). A new core network for the 5G System is referred to as a 5G CoreNetwork (5G-CN) or a NextGen Core (NG Core). A radio terminal (i.e.,User Equipment (UE)) capable of being connected to the 5G System isreferred to as 5G UE or NextGen UE (NG UE), or simply referred to as UE.The official names of the RAT, UE, radio access network, core network,network entities (nodes), protocol layers and the like for the NG Systemwill be determined in the future as standardization work progresses.

The term “LTE” used in this specification includes enhancement/evolutionof LTE and LTE-Advanced to provide interworking with the 5G System,unless otherwise specified. The enhancement/evolution of LTE andLTE-Advanced for the interworking with the 5G System is referred to asLTE-Advanced Pro, LTE+, or enhanced LTE (eLTE). Further, terms relatedto LTE networks and logical entities used in this specification, such as“Evolved Packet Core (EPC)”, “Mobility Management Entity (MME)”,“Serving Gateway (S-GW)”, and “Packet Data Network (PDN) Gateway(P-GW))”, include their enhancement/evolution to provide interworkingwith the 5G System, unless otherwise specified. Enhanced EPC, enhancedMME, enhanced S-GW, and enhanced P-GW are referred to, for example, asenhanced EPC (eEPC), enhanced MME (eMME), enhanced S-GW (eS-GW), andenhanced P-GW (eP-GW), respectively.

In LTE and LTE-Advanced, for achieving Quality of Service (QoS) andpacket routing, a bearer per QoS class and per PDN connection is used inboth a RAN (i.e., an Evolved Universal Terrestrial RAN (E-UTRAN)) and acore network (i.e., EPC). That is, in the Bearer-based QoS (orper-bearer QoS) concept, one or more Evolved Packet System (EPS) bearersare configured between a UE and a P-GW in an EPC, and a plurality ofService Data Flows (SDFs) having the same QoS class are transferredthrough one EPS bearer satisfying this QoS. An SDF is one or more packetflows that match an SDF template (i.e., packet filters) based on aPolicy and Charging Control (PCC) rule. In order to achieve packetrouting, each packet to be transferred through an EPS bearer containsinformation for identifying which bearer (i.e., General Packet RadioService (GPRS) Tunneling Protocol (GTP) tunnel) the packet is associatedwith.

In contrast, with regard to the 5G System, it is discussed that althoughradio bearers may be used in the 5G-RAN, no bearers are used in the5G-CN or in the interface between the 5G-CN and the NG-RAN (seeNon-Patent Literature 1). Specifically, PDU flows are defined instead ofan EPS bearer, and one or more SDFs are mapped to one or more PDU flows.A PDU flow between a 5G UE and a user-plane terminating entity in an NGCore (i.e., an entity corresponding to a P-GW in the EPC) corresponds toan EPS bearer in the EPS Bearer-based QoS concept. That is, the 5GSystem adopts the Flow-based QoS (or per-flow QoS) concept instead ofthe Bearer-based QoS concept. In the Flow-based QoS concept, QoS ishandled per PDU flow. The PDU flow is also referred to as a QoS flowaccordingly. Association between a 5G UE and a data network is referredto as a “PDU session”. The term “PDU session” corresponds to the term“PDN connection” in LTE and LTE-Advanced. A plurality of PDU flows (orQoS flows) can be configured in one PDU session.

It has also been suggested that the 5G System supports network slicing(see Non Patent Literature 1). Network slicing uses Network FunctionVirtualization (NFV) and software-defined networking (SDN) techniquesand makes it possible to create a plurality of virtualized logicalnetworks on a physical network. Each virtualized logical network isreferred to as a network slice or a network slice instance, includeslogical nodes and functions, and is used for specific traffic andsignaling. The 5G-RAN or the 5G-CN or both have a Slice SelectionFunction (SSF). The SSF selects one or more network slices suitable fora 5G UE based on information provided by at least one of the 5G UE andthe 5G-CN.

FIG. 1 shows a basic architecture of the 5G system. A UE establishes oneor more Signalling Radio Bearers (SRBs) and one or more Data RadioBearers (DRBs) with a gNB. The 5G-CN and the gNB establish a controlplane interface and a user plane interface for the UE. The control planeinterface between the 5G-CN and the gNB (i.e., RAN) is referred to as anNG2 interface or an NG-c interface and is used for transfer ofNon-Access Stratum (NAS) information and for transfer of controlinformation between the 5G-CN and the gNB. The user plane interfacebetween the 5G-CN and the gNB (i.e., RAN) is referred to as an NG3interface or an NG-u interface and is used for transfer of packets ofone or more PDU flows (or QoS flows) in a PDU session of the UE.

Furthermore, in the 5G System, a new RRC state is introduced in additionto the existing RRC_CONNECTED and RRC_IDLE states (see, for example, NonPatent Literature 1 to 5). The new RRC state is referred to as anRRC_INACTIVE state or an RRC_INACTIVE_CONNECTED state.

The RRC_CONNECTED and RRC_IDLE states of the 5G system have featuressimilar to those of the RRC_CONNECTED and RRC_IDLE states of LTE,respectively. When the UE is in the RRC_CONNECTED state, the UE and the5G-RAN maintain an AS context, and a location of the UE is known to the5G-RAN at cell level. Mobility of the UE in the RRC_CONNECTED state ishandled by a handover controlled by the 5G-RAN. On the other hand, whenthe UE is in the RRC_IDLE state, the UE and the 5G-RAN have released theAS context, the location of the UE is not known to the 5G-RAN, and thelocation of the UE is known to the 5G-CN at location registration arealevel. The location registration area corresponds to a Tracking Area(TA) of LTE. Mobility of the UE in the RRC_IDLE state is handled by cellreselection controlled by the UE. Moreover, the RRC state of the ASlayer is associated with a connection management (NG ConnectionManagement (NG CM)) state of the NAS layer. The UE in the RRC_CONNECTEDstate is considered to be in an NG-CM-CONNECTED state in the UE and the5G-CN. In contrast, the UE in the RRC_IDLE state is considered to be inan NG-CM-IDLE state in the UE and the 5G-CN.

It can be said that the RRC_INACTIVE state is an intermediate statebetween the RRC_CONNETED state and the RRC_IDLE state. Some features ofthe RRC_INACTIVE state are similar to those of the RRC_CONNETED state,while some other features of the RRC_INACTIVE state are similar to thoseof the RRC_IDLE state.

When the UE is in the RRC_INACTIVE state, the UE and the 5G-RAN maintainat least part of the AS context. The AS context held by the UE and the5G-RAN for the UE in the RRC_INACTIVE state includes, for example, aradio bearer configuration and an AS security context. Further, the5G-RAN keeps the control-plane and user-plane connections (i.e., NG2 andNG3 interfaces in FIG. 1 ) with the 5G-CN for the UE in the RRC_INACTIVEstate established. The UE in the RRC_INACTIVE state is considered to bein the NG-CM-CONNECTED state in the UE and the 5G-CN. Accordingly, the5G-CN does not distinguish whether the UE is in the RRC_CONNECTED stateor the RRC_INACTIVE state. These features of the RRC_INACTIVE state aresimilar to those of the RRC_CONNETED state.

However, the mobility of the UE in the RRC_INACTIVE state is similar tothat of the UE in the RRC_IDLE state. Specifically, the mobility of theUE in the RRC_INACTIVE state is handled by the cell reselectioncontrolled by the UE.

FIG. 2 shows state transitions, which are currently proposed, betweenthe three RRC states. The UE can transition from the RRC_CONNECTED stateto the RRC_INACTIVE state and vice versa (Steps 201 and 202). It isassumed that the transition between the RRC_CONNECTED state and theRRC_INACTIVE state reuses the Suspend and Resume procedures of the RRCConnection defined for LTE in 3GPP Release 13. The AS context stored inthe 5G-RAN for the UE in the RRC_INACTIVE state may be transferredbetween RAN nodes (i.e., gNBs). Specifically, when the UE transitionsfrom the RRC_INACTIVE state to the RRC_CONNECTED state, the gNB whichhas received an RRC message (e.g., RRC Connection Resume request) fromthe UE may fetch or retrieve the AS context of this UE from another gNB.

The location of the UE in the RRC_INACTIVE state is known to the 5G-RANat a level of a newly defined RAN Notification Area (RNA). The RANnotification area is also referred to as a RAN-based Notification Area,a RAN paging area, or a RAN location update area. The RAN notificationarea (RNA) includes one or more cells, is determined by the 5G-RAN, andis configured in the UE by the 5G-RAN. Even when the UE in theRRC_INACTIVE state moves between cells by cell reselection within theRAN notification area, there is no need to notify (or report to) the5G-RAN that it has performed the cell reselection. The UE in theRRC_INACTIVE state requests the 5G-RAN to update the RAN notificationarea in response to reselecting a cell outside the RAN notificationarea.

FIG. 3 shows an example of the mobility of the UE in the RRC_INACTIVEstate. First, a UE 301 is in the RRC_CONNECTED state (321) in a cell 351of a gNB 311 and it has been assigned dedicated radio resources from thegNB 311 and has established dedicated radio bearers 322. Upondetermining to move the UE 301 into the RRC_INACTIVE state, the gNB 311configures the UE 301 with a RAN notification area 340 and transmits anRRC message (e.g., RRC Suspend message) to the UE 301 (323). In responseto the instruction from the gNB 311, the UE 301 enters the RRC_INACTIVEstate from the RRC_CONNECTED state (324).

The UE 301 in the RRC_INACTIVE state performs a cell reselectionprocedure and accordingly reselects a cell 352 of a gNB 312 (325). Sincethe cell 352 is included in the RAN notification area 340 configured inthe UE 301, the UE 301 does not report the cell reselection (i.e.,update of UE location information) to the 5G-RAN (e.g., cell 352 or gNB312). The UE 301 further moves and reselects a cell 353 of a gNB 313(326). The cell 353 is not included in the RAN notification area 340configured in the UE 301, and accordingly the UE 301 transmits a requestfor a RAN notification area update (327) to the gNB 313. The request(327) may be transmitted using an RRC message (e.g., RRC Resume Requestmessage) requesting a transition from RRC_INACTIVE to RRC_CONNECTED. ThegNB 313 acquires an AS context of the UE 301 from the gNB 311 andre-establishes the Packet Data Convergence Protocol (PDCP) and RadioLink Control (RLC) for radio bearers using the acquired AS context.Then, the gNB 313 transmits an RRC message (e.g., RRC resume message) tomove the UE 301 to the RRC_CONNECTED state. In response to theinstruction from the gNB 311, the UE 301 enters the RRC_CONNECTED statefrom the RRC_INACTIVE state in the cell 353 (329). The UE 301 is able totransmit and receive data using dedicated radio bearers 330.

CITATION LIST Non Patent Literature

-   [Non-Patent Literature 1] 3GPP TR 23.799 V14.0.0 (2016-12) “3rd    Generation Partnership Project; Technical Specification Group    Services and System Aspects; Study on Architecture for Next    Generation System (Release 14)”, December 2016

SUMMARY OF INVENTION Technical Problem

The present inventor has conducted studies on mobility of a UE in theRRC_INACTIVE state and found some problems. For example, the mobility ofthe UE in the RRC_INACTIVE state may require considerations over networkslices. This is because a desired network slice might not be availablein a reselected cell in some cases. The network slice desired by the UEis, for example, a network slice that had been selected (or configured)by the network for this UE when the UE was in the RRC_CONNECTED statebefore it has entered the RRC_INACTIVE state.

In an example shown in FIG. 4 , a 5G-CN 430 includes Common NetworkFunctions (NFs) 431, Network Functions for Network Slice A (NFs forslice A) 432, and Network Functions for Network Slice B (NFs for sliceB) 433. The Common NFs 431 include a Common Control plane NetworkFunction (CCNF) and may further include a Common User plane NetworkFunction (CUNF). The NFs for slice A432 include a Slice-specificUser-plane Network Function (SUNF) and may further includeSlice-specific Control-plane NF (SCNF). Likewise, the NFs for slice B433includes an SUNF and may further include an SCNF.

In the example of FIG. 4 , gNBs 411 and 412 are both connected to theCommon NFs 431, the NFs for slice A432, and the NFs for slice B433.Meanwhile, a gNB 413 is connected to the Common NFs 431 and the NFs forslice A432, but it is not connected to the NFs for slice B433. That is,the network slice B is not available in a cell 423 of the gNB 413.

In the example of FIG. 4 , first, a UE 401 is in the RRC_CONNECTED statein a cell 421 of the gNB 411 and has been configured with the networkslice B. The UE 401 thus transmits and receives data through the networkslice B. After that, the UE 401 is configured with a RAN notificationarea 440 by the gNB 411 and enters the RRC_INACTIVE state. Furthermore,the UE 401 performs cell reselection (452). However, one problem is thathow the UE 401 in the RRC_INACTIVE state can know whether a desirednetwork slice is available in a target cell (i.e., a cell to bereselected or a reselected cell).

As an example, it may be preferable that the UE in the RRC_INACTIVEstate be able to determine whether the desired network slice isavailable in the reselected cell. If the UE can be aware that thedesired network slice is available in the reselected cell, the UE in theRRC_INACTIVE state can be allowed to remain the RRC_INACTIVE state inthe reselected cell without performing any special operation. On theother hand, if it is unknown whether the desired network slice isavailable in the reselected cell, the UE can immediately enter theRRC_CONNECTED state in the reselected cell and request the network forthe use of the network slice. Alternatively, if the UE in theRRC_INACTIVE state can know that the desired network slice isunavailable in the cell to be reselected or in the reselected cell, theUE can further reselect another cell.

Accordingly, one of the objects to be attained by embodiments disclosedherein is to provide an apparatus, a method, and a program that allow aUE in RRC_INACTIVE state to be easily aware of the availability ofnetwork slices in a target cell, i.e., a cell to be reselected or areselected cell. It should be noted that this object is merely one ofthe objects to be attained by the embodiments disclosed herein. Otherobjects or problems and novel features will be made apparent from thefollowing description and the accompanying drawings.

Solution to Problem

In a first aspect, a base station includes a memory and at least oneprocessor couple to the memory. The at least one processor is configuredto control state transitions of a first radio terminal among first tothird RRC states. The first RRC state is a state in which the firstradio terminal and the RAN maintain an access stratum (AS) context andin which a location of the first radio terminal is known to the RAN atcell level. The second RRC state is a state in which the first radioterminal and the RAN maintain at least part of the AS context and inwhich the location of the first radio terminal is known to the RAN atRAN notification area level configured by the RAN. The third RRC stateis a state in which the first radio terminal and the RAN have releasedthe AS context and in which the location of the first radio terminal isnot known to the RAN. The at least one processor is further configuredto explicitly or implicitly inform the first radio terminal aboutwhether a first network slice configured in the first radio terminal fordata communication at least in the first RRC state is available in eachcell included in the RAN notification area.

In a second aspect, a base station includes a memory and at least oneprocessor couple to the memory. The at least one processor is configuredto control state transitions of a first radio terminal among first tothird RRC states. The at least one processor is further configured totransmit, in a first cell of the base station, system informationindicating one or more network slices available or unavailable in thefirst cell.

In a third aspect, a radio terminal includes a transceiver and at leastone processor. The at least one processor is configured to control thetransceiver in one or more cells associated with a radio access network(RAN). The at least one processor is configured to control statetransitions of the radio terminal among first to third RRC states. Theat least one processor is further configured to check whether a firstnetwork slice configured in the radio terminal for data communication atleast in the first RRC state is available in a cell to be reselected bycell reselection in the second RRC state.

In a fourth aspect, a method for a base station placed in a Radio AccessNetwork (RAN) includes: (a) controlling state transitions of a firstradio terminal among first to third RRC states; and (b) explicitly orimplicitly informing the first radio terminal about whether a firstnetwork slice configured in the first radio terminal for datacommunication at least in the first RRC state is available in each cellincluded in a RAN notification area configured by the RAN.

In a fifth aspect, a method for a base station placed in a Radio AccessNetwork (RAN) includes: (a) controlling state transitions of a radioterminal among first to third RRC states; and (b) transmitting, in afirst cell of the base station, system information indicating one ormore network slices available or unavailable in the first cell.

In a sixth aspect, a method for a radio terminal includes: (a)controlling state transitions of the radio terminal among first to thirdRRC states; and (b) checking whether a first network slice configured inthe radio terminal for data communication at least in the first RRCstate is available in a cell to be reselected by cell reselection in thesecond RRC state.

In a seventh aspect, a program includes instructions (software codes)that, when loaded into a computer, cause the computer to perform themethod according to one of the above-described fourth to sixth aspects.

Advantageous Effects of Invention

According to the above-deceived aspects, it is possible to provide anapparatus, a method, and a program that allow a UE in RRC_INACTIVE stateto be easily aware of the availability of network slices in a targetcell, i.e., a cell to be reselected or a reselected cell.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing basic architecture of the 5G Systemaccording to the Background Art;

FIG. 2 is a diagram showing state transition among the three RRC statesin the 5G system according to the Background Art;

FIG. 3 is a diagram showing one example of mobility of a UE inRRC_INACTIVE state according to the Background Art;

FIG. 4 is a diagram for explaining a problem identified by the inventorsregarding the mobility of a UE in RRC_INACTIVE state;

FIG. 5 is a diagram showing a configuration example of a radiocommunication network according to a plurality of embodiments;

FIG. 6 is a sequence diagram showing an example of information exchangebetween gNBs according to a first embodiment;

FIG. 7 is a flowchart showing an example of an operation of a gNBaccording to the first embodiment;

FIG. 8 is a flowchart showing an example of an operation of a UEaccording to the first embodiment;

FIG. 9 is a flowchart showing an example of an operation of a UEaccording to the first embodiment;

FIG. 10 is a flowchart showing an example of an operation of a gNBaccording to a second embodiment;

FIG. 11 is a flowchart showing an example of an operation of a UEaccording to the second embodiment;

FIG. 12 is a sequence diagram showing an example of operations of a gNBand a UE according to a third embodiment;

FIG. 13 is a sequence diagram showing an example of operations of a gNBand a UE according to the third embodiment;

FIG. 14 is a flowchart showing an example of an operation of a UEaccording to the third embodiment;

FIG. 15 is a block diagram showing a configuration example of a gNBaccording to a plurality of embodiments; and

FIG. 16 is a block diagram showing a configuration example of a UEaccording to a plurality of embodiments.

DESCRIPTION OF EMBODIMENTS

Specific embodiments will be described hereinafter in detail withreference to the drawings. The same or corresponding elements aredenoted by the same symbols throughout the drawings, and duplicatedexplanations are omitted as necessary for the sake of clarity.

Each of the embodiments described below may be used individually, or twoor more of the embodiments may be appropriately combined with oneanother. These embodiments include novel features different from eachother. Accordingly, these embodiments contribute to attaining objects orsolving problems different from one another and contribute to obtainingadvantages different from one another.

The following descriptions on the embodiments mainly focus on a 5Gsystem that supports network slicing and uses an RRC_INACTIVE state.However, these embodiments may be applied to other radio communicationsystems supporting network slicing and using an RRC_INACTIVE state or asimilar RRC state.

First Embodiment

FIG. 5 shows a configuration example of a radio communication networkaccording to a plurality of embodiments including this embodiment. Inthe example of FIG. 5 , the radio communication network includes a 5G UE2, a 5G-RAN 3, and a 5G-CN 4.

The 5G-CN 4 includes Control Plane Network Functions (CP NFs) and UserPlane Network Functions (UP NFs), which are not shown, and provides aplurality of network slices. The network slices are distinguished fromone another according to, for example, services or use cases provided toUEs on each of the network slices. The use cases include, for example,enhanced Mobile Broad Band (eMBB), Ultra Reliable and Low LatencyCommunication (URLLC), and massive Machine Type Communication (mMTC).

The 5G-RAN 3 includes a plurality of gNBs, including a gNB 1A and a gNB1B. Each gNB 1 (e.g., gNB 1A and gNB 1B) serves at least one cell 11(e.g., cell 11A and cell 11B). Each gNB 1 is connected to the 5G-CN 4and supports one or more network slices. In other words, one or morenetwork slices are supported or available in the cell 11 of each gNB 1.In some implementations, in order to provide end-to-end network slicingto the UE 2, the 5G-RAN 3 assigns, to the UE 2, a RAN slice and a radioslice associated with a network slice of the 5G-CN 4 (referred to as aCore Network (CN) slice) selected for the UE 2. Each RAN slice providesstorage and processing resources of the infrastructures within the5G-RAN 3 including the gNB 1. Each radio slice provides radio resourcesincluding time resources, frequency resources, code resources, signalsequence resources, or spatial resources, or any combination thereof.

The UE 2 uses one or more cells 11 served by one or more gNBs 1 foruplink and downlink communication. The UE 2 supports a plurality of RRCstates including the RRC_CONNECTED state, the RRC_INACTIVE state, andthe RRC_IDLE state. The 5G-RAN 3 (gNB 1) and the UE 2 control statetransitions of the UE 2 among the RRC states including theRRC_CONNECTED, RRC_INACTIVE, and RRC_IDLE states.

For example, when the gNB 1A moves the UE 2 from the RRC_CONNECTED stateto the RRC_INACTIVE state, it transmits, to the UE 2, RAN notificationarea information via an RRC message (e.g., RRC Connection Release, RRCConnection Suspend, or RRC Connection Deactivate) to configure the RANnotification area in the UE 2. The RAN notification area includes one ormore cells served by one or more gNBs 1. The UE 2 enters theRRC_INACTIVE state in response to receiving the RRC message from the gNB1A. The UE 2 in the RRC_INACTIVE state moves between cells by cellreselection controlled by the UE 2, and does not need to report the cellreselection (i.e., update of UE location information) within the RANnotification area to the 5G-RAN 3. In contrast, in response toreselecting a cell (e.g., cell 11B) outside the configured RANnotification area, the UE 2 requests the gNB 1B serving the reselectedcell 11B to update the RAN notification area (or notify the gNB 1B thatit has left the configured RAN notification area). The gNB 1B determinesa new RAN notification area for the UE 2, and configures the determinedRAN notification area in the UE 2. That is, as described above, thelocation of the UE 2 in the RRC_INACTIVE state is known to the 5G-RAN 3at RAN notification area level.

As already described, the RAN notification area (RNA) includes one ormore cells, is determined by the 5G-RAN 3, and is configured in the UE 2by the 5G-RAN 3. The RAN notification area is also referred to as aRAN-based Notification Area, a RAN paging area, or a RAN location updatearea.

The RAN notification area information may include at least, for example,information indicating which cells are included in the RAN notificationarea. In addition, the RAN notification area may be assigned anidentifier (e.g., area number). Furthermore, the relationship between anidentifier of the RAN notification area (e.g., RNA ID) and the cell(s)contained therein may be determined uniquely within a predeterminedarea. In this case, the RAN notification area information may include anidentifier of the RAN notification area and information regarding thecontained cell(s) (e.g., cell identifier(s)).

The gNB 1A may broadcast the RAN notification area information in itscell 11A. At this time, the RAN notification area information mayinclude information relating to a plurality of RAN notification areas,they may be assigned their respective conditions (e.g., category, type),and the UE 2 may select one RAN notification area suitable for the UE 2.The condition is, for example, a slice category or slice type (e.g.,Slice/Service Type (SST)) of a network slice used (or desired) by the UE2, a terminal category or terminal type, reception quality at the UE 2or a coverage level based thereon, mobility characteristics of the UE 2(e.g., UE speed, whether it is a stationary terminal), or anycombination thereof.

The RAN notification area configured in the UE 2 may be the same as thelocation registration area of the UE 2 (i.e., area corresponding to theTracking Area (TA) in LTE). When each individual RAN notification area(i.e., Slice specific RNA) is configured for each network slice, atleast one of the RAN notification areas may be the same as the locationregistration area (e.g., TA). When the RNA is the same as the TA, aninformation element (e.g., RanAreaCellList Information Element (IE))indicating a cell list included in this RNA may be omitted from the RANnotification area information transmitted from the gNB 1 to the UE 2(that is, an Optional IE). Alternatively, the RAN notification areainformation may include an information element (e.g., TrackingAreaCodeIE) indicating a TA identifier instead of the information elementindicating the cell list (that is, Choice). In other words, the gNB 1may select one of the RanAreaCellList IE and the TrackingAreaCode IE toindicate the RAN notification area.

In order to transmit the RAN notification area information includinginformation relating to the plurality of RAN notification areas, the gNB1A may receive RAN notification area information (e.g., combination ofthe identifier of a RAN notification area and the identifiers of cellsconstituting this RAN notification area) from another gNB (e.g., gNB 1B)through an inter-gNB interface (Xn). The other gNB may manage a cellbelonging to another RAN notification area different from that to whichthe cell (e.g., cell 11A) of the gNB 1A belongs. Likewise, the RANnotification area-related information received from the other gNB mayrelate to another RAN notification area different from that to which thecell (e.g., cell 11A) of the gNB 1A belongs.

When the UE 2 uses (or desires) a plurality of network slices, it mayselect one RAN notification area based on the network slice having thehighest priority or based on the network slice that is actually beingused. Alternatively, the UE 2 may select one RAN notification area basedon the network slice that is high on the list of network slicecategories or types contained in the RAN notification area information.

The above-described RAN notification area information may include a RANnotification area (e.g., default RAN notification area) whose individualinformation (e.g., identifier, category, or type) is not explicitlyspecified. In this case, for example, the default RAN notification areamay be used for the UE 2 regardless of the network slice, or may be usedfor network slices other than those explicitly indicated in the RANnotification area information. Furthermore, when the RAN notificationarea information includes a plurality of RAN notification areas, the UE2 may not need to transmit to the gNB 1 a request for updating itslocation information as long as the cell after the cell reselection isincluded in at least one of the RAN notification areas.

Instead of the above-described instruction via the RRC message, the gNB1 may notify the UE 2 about a value of a predetermined timer whichtriggers the transition to the RRC_INACTIVE state, to cause the UE 2 toexecute the transition to the RRC_INACTIVE state based on the timervalue and the corresponding timer. For example, the UE 2 in theRRC_CONNECTED state may restart the timer (i.e., reset the timer andstart it again) each time it transmits or receives user data, and maytransition to the RRC_INACTIVE state when the timer expires.

The following describes the mobility of the UE 2 in the RRC_INACTIVEstate according to this embodiment. The gNB 1 according to thisembodiment is configured to explicitly inform the UE 2 about whether oneor more network slices configured in (or selected for) the UE 2 for datacommunication at least in the RRC_CONNECTED state are available in eachcell included in the RAN notification area for the UE 2. Morespecifically, in this embodiment, the gNB 1 is configured to transmit,to the UE 2, information explicitly indicating whether one or morenetwork slices configured in the UE 2 are available in each cell or eachgroup of cells included in the RAN notification area, which ishereinafter referred to as “slice availability information”. Instead ofthe slice availability information, the gNB 1 may transmit, to the UE 2,information explicitly indicating whether the slices are supported,which is hereinafter referred to as “slice support information”. Theslice availability information or the slice support information mayindicate one or more kinds (e.g., categories, types) of network slicesavailable (or supported) in the RAN notification area or in one or morecells included in the RAN notification area. Hereinafter, although theslice availability information is described as an example, the slicesupport information may be used instead.

In some implementations, the gNB 1 may transmit the slice availabilityinformation to the UE 2 when configuring the RAN notification area inthe UE 2. The slice availability information may be one informationelement associated with the RAN notification area (e.g., a list ofcells). Additionally or alternatively, the gNB 1 may transmit the sliceavailability information to the UE 2 during a procedure (e.g., an RRCmessage) in which the gNB 1 moves the UE 2 from the RRC_CONNECTED stateto the RRC_INACTIVE state.

FIG. 6 is a flowchart showing a process 600 that is an example of theoperation of the gNB 1. In Step 601, the gNB 1 creates sliceavailability information indicating whether the network slice used bythe UE 2 in the RRC_CONNECTED state is available in each cell includedin the RAN notification area. In Step 602, the gNB 1 transmits the sliceavailability information to the UE 2. The gNB 1 may transmit the sliceavailability information together with the RAN notification area (e.g.,a list of cells). In Step 603, the gNB 1 moves the UE 2 from theRRC_CONNECTED state to the RRC_INACTIVE state. As described above, thegNB 1 may transmit an instruction to move the UE 2 to the RRC_INACTIVEstate, together with the slice availability information.

Each gNB 1 needs to know the slice availability (or slice supportstatus) in other gNBs 1 or in each of the cells served by the other gNBs1. In some implementations, a network operator may configure, in eachgNB 1, the slice availability in the cells of the other gNBs 1 via anOperation and Management (O&M) server. Additionally or alternatively,each gNB 1 may communicate with another gNB 1 over the inter-gNBinterface (Xn) (e.g., Xn Setup Request/Response messages), therebydynamically acquiring the slice availability in the cells of the othergNB 1. When its slice availability has been changed (or updated), eachgNB 1 may notify other gNBs 1 of it (e.g., gNB Configuration Updatemessage). Additionally or alternatively, each gNB 1 may communicate withanother gNB 1 through the interface (NG2, NG-c) between the gNB 1 andthe 5G-CN 4, and dynamically acquire the slice availability in the cellsof the other gNB 1.

FIG. 7 is a sequence diagram showing a process 700 that is an example ofcommunication between two gNBs 1.

In Step 701, the gNB 1A sends, to the gNB 1B, information (e.g., NetworkSlice Availability Information) indicating network slices available ineach cell served by the gNB 1A. The gNB 1A may send this information inresponse to a request from the gNB 1B. Additionally or alternatively, inresponse to an update of the slice availability in any of the cellsserved by the gNB 1A, the gNB 1A may send the update to the gNB 1B.Additionally or alternatively, the gNB 1A may periodically send theslice availability in each cell to the gNB 1B. In Step 702, the gNB 1Bsends, to the gNB 1A, information (e.g., Network Slice AvailabilityInformation) indicating network slices available in each cell served bythe gNB 1B. Additionally or alternatively, the gNB 1A may send to thegNB 1B, through the interface (NG2, NG-c) with the core network (5G-CN4), the information (e.g., Network Slice Availability Information)indicating network slices available in each cell served by the gNB 1A.

Note that, as described above, the gNB 1A may exchange their RANnotification area information (e.g., combination of the identifier ofthe RAN notification area and the identifiers of the cells constitutingthe RAN notification area) with the gNB 1B through an inter-gNBinterface (Xn). In this case, the RAN notification area information mayindicate a RAN notification area to which the cell 11 of thetransmission source gNB 1 belongs, or instead indicate a RANnotification area to which the cell 11 of the transmission destinationgNB 1 should belong. That is, when the cells 11A and 11B managed by thegNB 1A and the gNB 1B, respectively, belong to (or should belong to)different RAN notification areas, the gNBs 1 may share the RANnotification area information with each other and recognize theplurality of RAN notification areas which should be included in the RANnotification area information to be transmitted to the UE 2.

The RAN notification area information communicated between the gNBs maybe included in the information (e.g., Network Slice AvailabilityInformation) indicating network slices available in each cell served bythe gNB 1A shown in FIG. 7 . On the other hand, the RAN notificationarea information communicated between the gNBs may include theinformation (e.g., Network Slice Availability Information) indicatingnetwork slices available in each cell served by the gNB 1A shown in FIG.7 .

In some implementations, the information indicating network slicesavailable in each cell served by the gNB 1A and the correspondinginformation regarding the gNB 1B may be sent from the core network(5G-CN 4) to the gNB 1B and the gNB 1A, respectively. In this case, the5G-CN needs to know in advance network slices available (or supported)in each gNB 1. For example, the 5G-CN 4 may specify, for each gNB 1,network slices available (or supported) in each gNB 1. Alternatively,the 5G-CN 4 may receive from each gNB 1 a report of network slicesavailable (or supported) in the gNB 1.

The UE 2 according to this embodiment is configured to check whether oneor more network slices that have been configured in (or allowed(authorized) or accepted for) the UE 2 for data communication at leastin the RRC_CONNECTED state are available in a cell to be reselected (ora reselected cell) by cell reselection in the RRC_INACTIVE state. Morespecifically, in this embodiment, the UE 2 is configured to receive theabove-described slice availability information from the gNB 1. The sliceavailability information explicitly indicates whether one or morenetwork slices configured in the UE 2 are available in each cellincluded in the RAN notification area for the UE 2.

FIG. 8 is a flowchart showing a process 800 that is an example of theoperation of the UE 2. In Step 801, the UE 2 is in the RRC_CONNECTEDstate and receives the above-described slice availability informationfrom the serving gNB 1. In Step 802, the UE 2 transitions from theRRC_CONNECTED state to the RRC_INACTIVE state in response to aninstruction from the serving gNB 1. In Step 803, the UE 2 in theRRC_INACTIVE state performs cell reselection. The UE 2 checks, based onthe slice availability information, whether a desired network slice(s)is available in the cell to be reselected (or in the reselected cell).The desired network slice(s) may be one or more network slices that hadbeen configured in (or allowed (authorized) or accepted for) the UE 2 bythe network (i.e., 5G-CN 4 or 5G-RAN 3 or both) when the UE 2 wasformerly in the RRC_CONNECTED state.

The following describes an example of the operation of the UE 2 afterchecking the network slice availability. FIG. 9 is a flowchart showing aprocess 900 that is an example of the operation of the UE 2. In Step901, the UE 2 checks the network slice availability in the cell to bereselected (or the reselected cell) by cell reselection in theRRC_INACTIVE state. If the desired network slice is available in thereselected cell, the UE 2 stays in that cell (continue to camp on thatcell).

If the desired network slice is not available in the reselected cell,the UE 2 performs a notification to the gNB 1 serving the reselectedcell about the desired network slice (Step 902). The notification may bea request for the desired network slice, for example, a request forconfiguring the desired network slice with the UE 2 (or providing thedesired network slice to the UE 2) or a request for moving (e.g.,handover, re-direction) to a cell where the desired network is available(or supported). When the UE 2 fails to confirm that the desired networkslice is available in the reselected cell, it may inform the gNB 1serving the reselected cell about the desired network slice. In otherwords, when it is unknown whether the desired network slice is availablein the reselected cell, the UE 2 may inform the gNB 1 serving thereselected cell about the desired network slice.

In some implementations, the UE 2 may transmit a notification about thedesired network slice after transitioning to the RRC_CONNECTED state.Alternatively, the UE 2 may transmit a notification about the desirednetwork slice while it is in the RRC_INACTIVE state. In other words, theUE 2 may transmit the notification without completely transitioning tothe RRC_CONNECTED state. Furthermore, in other words, the UE 2 maytransmit the notification before entering the RRC_CONNECTED state. Inone example, the UE 2 may transmit the notification during a procedurefor transitioning to the RRC_CONNECTED state. Specifically, the UE 2 maytransmit the notification using an RRC message (e.g., RRC ConnectionResume request or RRC Connection Activate) used for the transition tothe RRC_CONNECTED state. Alternatively, the UE 2 may transmit thenotification about the desired network slice using a signal that can betransmitted while remaining in the RRC_INACTIVE state (e.g., PRACHpreamble, RACH data, UL reference signal, MAC Control Element (CE)), oran RRC message (e.g., UL Information Transfer, UL Direct Information, orUE Assistance Information)). At this time, the signal or message may betransmitted using a dedicated radio resource that the UE 2 has notifiedof (or configured with) in advance, or using a radio resource sharedamong a plurality of UEs 2. In the latter case, for example, the UE 2may transmit the notification about the desired network slice in atransmission scheme in which a separate grant for uplink transmission isnot required (i.e., grant-free). The RRC message may be transmitted, forexample, in the first step uplink transmission (e.g., RACH data) in anew random access procedure for NR. The new random access procedure forNR may be a procedure which is a Contention-based Random Accessprocedure including a total of two steps, which has been simplified fromthat in LTE including a total of four steps. The UE 2 may be configuredin advance by the gNB 1 with either the two-step random access or thefour-step random access. Alternatively, the UE 2 may perform one of therandom access procedures that is allowed (or supported) in the cellafter the cell reselection. The UE 2 may determine whether the two-steprandom access or the four-step random access is allowed (or supported)according to whether configuration information regarding radio resourcesused therefor is transmitted in system information.

The notification about the desired network slice may be, for example,the UE 2 explicitly transmitting identification information (e.g., aunique identifier or temporary identifier of the network slice, a slicecategory of the network slice, or a slice type (e.g., Slice/Service Type(SST))) of the desired network slice. The identification informationregarding the desired network slice may be transmitted, for example, viaNetwork Slice Selection Assistance Information (NSSAI) contained in anRRC message or MAC Control Element. Additionally or alternatively, theidentification information regarding the desired network slice may beimplicitly transmitted using a predetermined signal sequence (e.g., RACHpreamble, UL reference signal) previously associated therewith, or apredetermined time, frequency, code, or space radio resources previouslyassociated therewith. The gNB 1 may broadcast, in its cell, informationregarding association between the identification information regardingthe desired network slice and the signal sequence or radio resource, ormay individually notify the UE 2 of it. When the gNB 1 broadcasts theinformation regarding the association, the UE 2 may receive (or monitor)it in a reselected target cell after reselection. Furthermore, when aplurality of network nodes (e.g., Network Slice Instance (NSI)) support(or provide) the same slice type, the gNB 1 or the 5G-CN may configure,in the UE 2, identifiers (e.g., Slice Differentiators (SDs)) fordistinguishing these network nodes in the UE 2. In this case, the UE 2may also explicitly or implicitly transmit this identifier via thenotification about the desired network slice.

After receiving the RRC message including the notification or the signalindicating the notification, the gNB 1 may move the UE 2 (i.e., maycause the UE 2 to transition) to the RRC_CONNECTED state, or may keepthe UE 2 in the RRC_INACTIVE state. In some implementations, the gNB 1may move the UE 2 to an appropriate cell when the network slicerequested by the UE 2 is not available in the gNB 1 or the cell thereof.Specifically, the gNB 1 may move the UE 2 to another cell in which thenetwork slice requested by the UE 2 is available (or supported). Theother cell to which UE 2 is to be moved may be another cell served bythe same gNB 1 as the cell (i.e., the cell reselected by the UE 2) inwhich the gNB 1 has received the notification about the desired networkslice from the UE 2. Alternatively, the other cell to which the UE 2 isto be moved may be a cell of another gNB 1. The gNB 1 may use a handoverprocedure or a redirection procedure (e.g., RRC connection release withredirection) to move the UE 2 to the appropriate cell.

When the UE 2 receives the RAN notification area information includingthe plurality of RAN notification areas and transmits uplink data (i.e.,there is uplink data to be transmitted) in the cell after the cellreselection, it may operate as follows. The UE 2 may determine whetherthe network slice to which the uplink data belongs (or with which theuplink data is associated) is available (or supported) in the celldepending on whether the RAN notification area in which the cell isincluded corresponds to the network slice, or whether the RANnotification area corresponding to the network slice includes the cell.For example, when the RAN notification area corresponding to the networkslice to which the uplink data to be transmitted belongs (or the networkslice associated therewith) includes the cell after the cellreselection, the UE 2 may transmit the uplink data. Otherwise, the UE 2may notify the gNB 1 of the desired network slice.

As can be understood from the above description, the gNB 1 according tothis embodiment is configured to transmit the slice availabilityinformation to the UE 2. The slice availability information indicateswhether one or more network slices configured in (or selected for) theUE 2 for data communication at least in the RRC_CONNECTED state areavailable in each cell included in the RAN notification area for the UE2. Accordingly, the slice availability information enables the UE 2 tocheck whether the desired network slice is available in the cell to bereselected (or in the reselected cell) by cell reselection in theRRC_INACTIVE state. Thus, this embodiment can facilitate the UE 2 in theRRC_INACTIVE state to know the availability of the network slice in thecell to be reselected or in the reselected cell.

Second Embodiment

This embodiment provides a modified example of the mobility of the UE 2in the RRC_INACTIVE state. A configuration example of the radiocommunication network according to this embodiment is similar to that ofFIG. 5 .

The gNB 1 according to this embodiment is configured to implicitlyinform the UE 2 about whether one or more network slices configured in(or selected, allowed, or accepted for) the UE 2 for data communicationat least in the RRC_CONNECTED state are available in each cell includedin the RAN notification area for the UE 2. More specifically, in thisembodiment, the gNB 1 is configured to include, in the RAN notificationarea for the UE 2 in the RRC_INACTIVE state, only one or more cells inwhich the network slice configured for the UE 2 in the RRC_CONNECTEDstate is available (or supported), and to configure the RAN notificationarea in the UE 2. Thus, the RAN notification area implicitly indicatesthat the network slice configured in the UE 2 is available in each cellincluded in the RAN notification area.

FIG. 10 is a flowchart showing a process 1000 that is an example of theoperation of the gNB 1. In Step 1001, the gNB 1 includes, in the RANnotification area, only one or more cells in which the network slicethat have been configured in the UE 2 in the RRC_CONNECTED state isavailable. In Step 1002, the gNB 1 notifies the UE 2 of the determinedRAN notification area. In Step 1003, the gNB 1 moves the UE 2 from theRRC_CONNECTED state to the RRC_INACTIVE state.

FIG. 11 is a flowchart showing a process 1100 that is an example of theoperation of the UE 2. In Step 1101, the UE 2 is in the RRC_CONNECTEDstate and receives the configuration of the RAN notification area fromthe serving gNB 1. This RAN notification area includes only one or morecells in which the network slice that have been configured in the UE 2is available. In Step 1102, the UE 2 transitions from the RRC_CONNECTEDstate to the RRC_INACTIVE state in response to an instruction from theserving gNB 1. In Step 1103, the UE 2 in the RRC_INACTIVE state performscell reselection. The UE 2 checks whether a desired network slice(s) isavailable in the cell to be reselected depending on whether the cell tobe reselected is included in the RAN notification area. Here, thedesired network slice(s) may be one or more network slices that had beenconfigured in (or allowed or accepted for) the UE 2 by the network(i.e., 5G-CN 4 or 5G-RAN 3 or both) when the UE 2 was formerly in theRRC_CONNECTED state.

The operations of the UE 2 and the gNB 1 after the UE 2 checks thenetwork slice availability may be similar to that of the exampledescribed in the first embodiment.

The gNB 1 may configure a plurality of RAN notification areas in the UE2 and may transmit the RAN notification area information including theplurality of RAN notification areas to the UE 2. At least one of the RANnotification areas included in the RAN notification area information maybe determined to include only one or more cells in which the networkslice configured (or selected, allowed, or accepted) for the UE 2 isavailable (or supported). For example, both the first and second RANnotification areas may be configured in the UE 2 and the first RANnotification area may only include one or more cells in which thenetwork slice configured (or selected, allowed, or accepted) for the UE2 is available (or supported), while the second RAN notification areamay include one or more cells in which the UE 2 can move (i.e., performcell reselection) without notifying the gNB 1. In this case, the secondRAN notification area may be configured in the UE 2 as a defaultconfiguration, whereas the first RAN notification area may be configuredin the UE 2 as an optional configuration. Specifically, the gNB 1 mayalways transmit the second RAN notification area to the UE 2 as the RANnotification area to be applied to the UE 2 regardless of the use of thenetwork slice. In contrast, the gNB 1 may transmit the first RANnotification area to the UE 2 only when the UE 2 uses the network sliceor is configured with the network slice.

Additionally or alternatively, the RAN notification area may beconfigured per slice category or slice type of the network slicesconfigured in (or selected, allowed, or accepted for) the UE 2. In oneexample, a correspondence between the plurality of RAN notificationareas and the plurality of network slices may be determined by aconfiguration order of the plurality of RAN notification areas and aconfiguration order of the plurality of network slices. Specifically,the RAN notification area having the first configuration order may beassociated with the first network slice having the first configurationorder. Alternatively, the correspondence between the plurality of RANnotification areas and the plurality of network slices may be determinedby the configuration order of the plurality of RAN notification areasand the ascending order of the identifiers of the plurality of networkslices. Specifically, the RAN notification area having the firstconfiguration order may be associated with the network slice having thesmallest identifier. When the number of the network slices configured inthe UE 2 excluding the above-mentioned default configuration (defaultRAN notification area) differs from the number of the RAN notificationareas configured in the UE 2, the UE 2 may apply the following handling.When the number of the configured network slices is larger than thenumber of the RAN notification areas, the UE 2 recognizes that remainingnetwork slices which cannot be associated with the RAN notificationareas are not available (or supported) in any cell other than theserving cell (i.e., the cell in which the UE 2 receives the RANnotification area information). On the other hand, when the number ofthe configured network slices is smaller than the number of the RANnotification areas, the UE 2 ignores the remaining RAN notificationareas which cannot be associated with the network slices.

As can be understood from the above description, the gNB 1 according tothis embodiment determines the RAN notification area including only oneor more cells in which one or more network slices configured in (orselected for) the UE 2 for data communication at least in theRRC_CONNECTED state, and notifies the UE 2 of the determined RANnotification area. Accordingly, the RAN notification area enables the UE2 to check whether the desired network slice is available in the cell tobe reselected (or in the reselected cell) by cell reselection in theRRC_INACTIVE state. Thus, this embodiment facilitates the UE 2 in theRRC_INACTIVE state to know the availability of the network slice in thecell to be reselected or in the reselected cell.

Third Embodiment

This embodiment provides a modified example of the mobility of the UE 2in the RRC_INACTIVE state. A configuration example of the radiocommunication network according to this embodiment is similar to that ofFIG. 5 .

The gNB 1 according to this embodiment is configured to transmit, ineach of its cells, System Information (SI) indicating one or morenetwork slices available (or supported) or unavailable (or notsupported) in the cell. The System information may be included in abroadcast system information block to be broadcast in each cell.Alternatively, the System information may be included in an on-demandsystem information block to be transmitted to the UE 2 in response to arequest message from the UE 2 or in response to a trigger inside thenetwork.

FIG. 12 is a sequence diagram showing a process 1200 that is an exampleof the operations of the gNB 1 and the UE 2 according to thisembodiment. In Step 1201, the UE 2 is in the RRC_INACTIVE state andperforms a cell reselection procedure. In Step 1202, the UE 2 receivessystem information from the gNB 1 in the cell to be reselected (or inthe reselected cell). The system information includes network sliceavailability information. The network slice availability informationindicates one or more network slices available or unavailable in thecell. As described above, the network slice availability information maybe included in on-demand system information block.

When the network slice availability information is a broadcast systeminformation block, the UE 2 may receive the broadcast system informationblock in the reselected cell in response to the cell reselection and maycheck the network slice availability in the reselected cell.

When the network slice availability information is an on-demand systeminformation block, for example, the gNB 1 broadcasts primary information(e.g., indication of system information on the network slicing, oravailability of network slicing SI) indicating that system informationindicating the network slice availability information is to betransmitted as an on-demand system information block. When the primaryinformation is transmitted as system information (e.g., Essential systeminformation of LTE, or Minimum system information of the NR) necessaryfor the UE 2 to access the cell, the UE 2 receives the primaryinformation before performing the cell reselection. Then, upon (or inresponse to) performing the cell reselection, the UE 2 requests the gNB1 to transmit the on-demand system information block. The gNB 1transmits the network slice availability information in response to therequest from the UE 2.

The UE 2 may immediately transmit the transmission request for theon-demand system information block in response to the cell reselection.Alternatively, the UE 2 may transmit the transmission request for theon-demand system information block when transitioning to theRRC_CONNECTED state due to an occurrence of the uplink data to betransmitted or for other purposes. Additionally or alternatively, the UE2 may transmit the transmission request for the on-demand systeminformation block while remaining in the RRC_INACTIVE state. When theprimary information is transmitted in other system information (i.e.,information other than the system information necessary for the UE 2 toaccess the cell), the UE 2 may receive the primary information after (orin response to) performing the cell reselection. In someimplementations, the UE 2 may transmit the transmission request for theon-demand system information block on a Random Access Channel (RACH), orvia dedicated signalling (e.g., RRC signalling or Medium Access Control(MAC) Control Element (CE)).

FIG. 13 is a sequence diagram showing a process 1300 that is an exampleof the operations of the gNB 1 and the UE 2 when the network sliceavailability information is the on-demand system information block. InStep 1301, the gNB 1 transmits the notification about availableon-demand system information. The notification about the availableon-demand system information corresponds to the above-described primaryinformation. The notification is necessary for the UE 2 to access thecell 11 of the gNB 1 and is included in the system information (e.g.,Essential SI, SIB1) which is broadcast in the cell 11 of the gNB 1.Alternatively, the notification about available on-demand systeminformation may be included in another SI that is not Essential SI.

In Step 1302, the UE 2 is in the RRC_INACTIVE state and performs a cellreselection procedure. The UE 2 checks the “notification about availableon-demand system information” included in the system informationreceived in Step 1301 and then sends a transmission request for theon-demand SI including the network slice information to the gNB 1 (Step1304). Note that when the notification about available on-demand systeminformation is included in another SI that is not the Essential SI, theUE 2 may receive the other SI (e.g., SIBx) after the cell reselection(Step 1303). Step 1303 is omitted when the notification about availableon-demand system information is included in the Essential SI (e.g.,SIB1). In Step 1305, the UE 2 receives the system information includingthe network slice availability information from the gNB 1.

FIG. 14 is a flowchart showing a process 1400 that is an example of theoperation of the UE 2. In Step 1401, in response to the cell reselectionin the RRC_INACTIVE state, the UE 2 attempts to receive the systeminformation including the network slice availability information in thereselected cell. In Step 1402, the UE 2 checks whether a desired networkslice(s) is available in the reselected cell based on the receivedsystem information. Here, the desired network slice(s) may be one ormore network slices that had been configured in (or allowed or acceptedfor) the UE 2 by the network (i.e., 5G-CN 4 or 5G-RAN 3 or both) whenthe UE 2 was formerly in the RRC_CONNECTED state.

The operations of the UE 2 and the gNB 1 after the UE 2 checks thenetwork slice availability may be similar to that of the exampledescribed in the first embodiment.

As can be understood from the above description, the gNB 1 according tothis embodiment transmits, in each cell, the system informationindicating the network slice availability in the cell. Accordingly, thesystem information enables the UE 2 to check whether the desired networkslice is available in the cell to be reselected (or in the reselectedcell) by cell reselection in the RRC_INACTIVE state. Thus, thisembodiment facilitates the UE 2 in the RRC_INACTIVE state to know theavailability of the network slice in the cell to be reselected or in thereselected cell.

Fourth Embodiment

This embodiment provides an operation when downlink user data addressedto the UE 2 in the RRC_INACTIVE state arrives at the network. Aconfiguration example of a radio communication network according to thisembodiment is similar to that of FIG. 5 .

When downlink user data addressed to the UE 2 in the RRC_INACTIVE statearrives at the 5G-CN 4, the 5G-CN 4 transfers the user data to the gNB 1(e.g., gNB 1A) to which the UE 2 had been connected at the time when theUE 2 was transitioned to the RRC_INACTIVE state. The gNB 1A transmits,in its cell 11A, a notification of arrival of the downlink user datasimilar to the existing paging (i.e., paging message), which is referredto as “RAN-based paging”. Furthermore, when the RAN notification area(RNA) configured in the UE 2 includes a cell of another gNB 1 (e.g., gNB1B), the gNB 1 informs the gNB 1B about the arrival of the downlink userdata for the UE 2 through the inter-gNB interface (Xn), which isreferred to as “Xn paging”. The Xn paging may include informationregarding the RAN notification area (RNA) to which the UE 2 belongs.Then, in a manner similar to the gNB 1A, the gNB 1B may transmit theRAN-based paging in its cell 11B which is included in the RNA.

The gNB 1A may include, into the Xn paging (i.e., the notification ofthe arrival of the downlink user data for the UE 2) to be transmitted tothe gNB 1B, information indicating one or more network slices which hadbeen configured in (or allowed or accepted for) the UE 2. This allowsthe gNB 1B to know the network slice(s) used (or desired) by the UE 2.

The gNB 1A may include, into the Xn paging (i.e., the notification ofthe arrival of the downlink user data for the UE 2) to be sent to thegNB 1B, information regarding the RAN notification area(s) that the UE 2has been configured with (or has been notified of). This allows the gNB1B to know the cell to which the RAN-based paging should be transmitted.

The following provides configuration examples of the gNB 1 and the UE 2according to the above embodiments. FIG. 15 is a block diagram showing aconfiguration example of the gNB 1 according to the above embodiments.Referring to FIG. 15 , the gNB 1 includes a Radio Frequency transceiver1501, a network interface 1503, a processor 1504, and a memory 1505. TheRF transceiver 1501 performs analog RF signal processing to communicatewith NG UEs including the UE 2. The RF transceiver 1501 may include aplurality of transceivers. The RF transceiver 1501 is coupled to anantenna array 1502 and the processor 1504. The RF transceiver 1501receives modulated symbol data from the processor 1504, generates atransmission RF signal, and supplies the transmission RF signal to theantenna array 1502. Further, the RF transceiver 1501 generates abaseband reception signal based on a reception RF signal received by theantenna array 1502 and supplies the baseband reception signal to theprocessor 1504. The RF transceiver 1501 may include an analog beamformercircuit for beam forming. The analog beamformer circuit includes, forexample, a plurality of phase shifters and a plurality of poweramplifiers.

The network interface 1503 is used to communicate with network nodes(e.g., a control node and a transfer node in the 5G-CN 4). The networkinterface 1503 may include, for example, a network interface card (NIC)conforming to the IEEE 802.3 series.

The processor 1504 performs digital baseband signal processing (i.e.,data-plane processing) and control-plane processing for radiocommunication. The processor 1504 may include a plurality of processors.The processor 1504 may include, for example, a modem processor (e.g., aDigital Signal Processor (DSP)) that performs digital baseband signalprocessing and a protocol stack processor (e.g., a Central ProcessingUnit (CPU) or a Micro Processing Unit (MPU)) that performs thecontrol-plane processing. The processor 1504 may include a digitalbeamformer module for beam forming. The digital beamformer module mayinclude a Multiple Input Multiple Output (MIMO) encoder and a pre-coder.

The memory 1505 is composed of a combination of a volatile memory and anon-volatile memory. The volatile memory is, for example, a StaticRandom Access Memory (SRAM), a Dynamic RAM (DRAM), or a combinationthereof. The non-volatile memory is, for example, a mask Read OnlyMemory (MROM), an Electrically Erasable Programmable ROM (EEPROM), aflash memory, a hard disc drive, or any combination thereof. The memory1505 may include a storage located apart from the processor 1504. Inthis case, the processor 1504 may access the memory 1505 via the networkinterface 1503 or an I/O interface (not shown).

The memory 1505 may store one or more software modules (computerprograms) 1506 including instructions and data to perform processing bythe gNB 1 described in the above embodiments. In some implementations,the processor 1504 may be configured to load the software modules 1506from the memory 1505 and execute the loaded software modules, therebyperforming processing of the gNB 1 described in the above embodiments.

FIG. 16 is a block diagram showing a configuration example of the UE 2.A Radio Frequency (RF) transceiver 1601 performs analog RF signalprocessing to communicate with the gNB 1. The RF transceiver 1601 mayinclude a plurality of transceivers. The analog RF signal processingperformed by the RF transceiver 1601 includes frequency up-conversion,frequency down-conversion, and amplification. The RF transceiver 1601 iscoupled to an antenna array 1602 and a baseband processor 1603. The RFtransceiver 1601 receives modulated symbol data (or OFDM symbol data)from the baseband processor 1603, generates a transmission RF signal,and supplies the transmission RF signal to the antenna array 1602.Further, the RF transceiver 1601 generates a baseband reception signalbased on a reception RF signal received by the antenna array 1602 andsupplies the baseband reception signal to the baseband processor 1603.The RF transceiver 1601 may include an analog beamformer circuit forbeam forming. The analog beamformer circuit includes, for example, aplurality of phase shifters and a plurality of power amplifiers.

The baseband processor 1603 performs digital baseband signal processing(i.e., data-plane processing) and control-plane processing for radiocommunication. The digital baseband signal processing includes (a) datacompression/decompression, (b) data segmentation/concatenation, (c)composition/decomposition of a transmission format (i.e., transmissionframe), (d) channel coding/decoding, (e) modulation (i.e., symbolmapping)/demodulation, and (f) generation of OFDM symbol data (i.e.,baseband OFDM signal) by Inverse Fast Fourier Transform (IFFT).Meanwhile, the control-plane processing includes communicationmanagement of layer 1 (e.g., transmission power control), layer 2 (e.g.,radio resource management and hybrid automatic repeat request (HARQ)processing), and layer 3 (e.g., signaling regarding attach, mobility,and call management).

The digital baseband signal processing by the baseband processor 1603may include, for example, signal processing of a Packet Data ConvergenceProtocol (PDCP) layer, a Radio Link Control (RLC) layer, a MAC layer,and a PHY layer. Further, the control-plane processing performed by thebaseband processor 1603 may include processing of a Non-Access Stratum(NAS) protocol, an RRC protocol, and MAC CEs.

The baseband processor 1603 may perform MIMO encoding and pre-coding forbeam forming.

The baseband processor 1603 may include a modem processor (e.g., DSP)that performs the digital baseband signal processing and a protocolstack processor (e.g., a CPU or an MPU) that performs the control-planeprocessing. In this case, the protocol stack processor, which performsthe control-plane processing, may be integrated with an applicationprocessor 1604 described in the following.

The application processor 1604 is also referred to as a CPU, an MPU, amicroprocessor, or a processor core. The application processor 1604 mayinclude a plurality of processors (processor cores). The applicationprocessor 1604 loads a system software program (Operating System (OS))and various application programs (e.g., a call application, a WEBbrowser, a mailer, a camera operation application, and a music playerapplication) from a memory 1606 or from another memory (not shown) andexecutes these programs, thereby providing various functions of the UE2.

In some implementations, as represented by a dashed line (1605) in FIG.16 , the baseband processor 1603 and the application processor 1604 maybe integrated on a single chip. In other words, the baseband processor1603 and the application processor 1604 may be implemented in a singleSystem on Chip (SoC) device 1605. An SoC device may be referred to as asystem Large Scale Integration (LSI) or a chipset.

The memory 1606 is a volatile memory, a non-volatile memory, or acombination thereof. The memory 1606 may include a plurality of memorydevices that are physically independent from each other. The volatilememory is, for example, an SRAM, a DRAM, or a combination thereof. Thenon-volatile memory is, for example, an MROM, an EEPROM, a flash memory,a hard disc drive, or any combination thereof. The memory 1606 mayinclude, for example, an external memory device that can be accessedfrom the baseband processor 1603, the application processor 1604, andthe SoC 1605. The memory 1606 may include an internal memory device thatis integrated in the baseband processor 1603, the application processor1604, or the SoC 1605. Further, the memory 1606 may include a memory ina Universal Integrated Circuit Card (UICC).

The memory 1606 may store one or more software modules (computerprograms) 1607 including instructions and data to perform the processingby the UE 2 described in the above embodiments. In some implementations,the baseband processor 1603 or the application processor 1604 may loadthese software modules 1607 from the memory 1606 and execute the loadedsoftware modules, thereby performing the processing of the UE 2described in the above embodiments with reference to the drawings.

As described above with reference to FIGS. 15 and 16 , each of theprocessors included in the gNB 1 and the UE 2 according to theabove-described embodiments executes one or more programs includinginstructions to cause a computer to perform an algorithm described withreference to the drawings. The program(s) can be stored and provided toa computer using any type of non-transitory computer readable media.Non-transitory computer readable media include any type of tangiblestorage media. Examples of non-transitory computer readable mediainclude magnetic storage media (such as flexible disks, magnetic tapes,hard disk drives, etc.), optical magnetic storage media (e.g.,magneto-optical disks), Compact Disc Read Only Memory (CD-ROM), CD-R,CD-R/W, and semiconductor memories (such as mask ROM, Programmable ROM(PROM), Erasable PROM (EPROM), flash ROM, Random Access Memory (RAM),etc.). The program(s) may be provided to a computer using any type oftransitory computer readable media. Examples of transitory computerreadable media include electric signals, optical signals, andelectromagnetic waves. Transitory computer readable media can providethe program to a computer via a wired communication line (e.g., electricwires, and optical fibers) or a wireless communication line.

Other Embodiments

The 5G-RAN 3 described in the above embodiments may be implemented basedon a Cloud Radio Access Network (C-RAN) concept. The C-RAN is alsoreferred to as a Centralized RAN. In this case, processes and operationsperformed by the gNB 1 described in the above embodiments may beprovided by a Digital Unit (DU) included in the C-RAN architecture, orby a combination of a DU and a Radio Unit (RU). The DU is also referredto as a Baseband Unit (BBU) or a Central Unit (CU). The RU is alsoreferred to as a Remote Radio Head (RRH), a Remote Radio Equipment(RRE), a Distributed Unit (DU), or a Transmission and Reception Point(TRP or TRxP). That is, processes and operations performed by the gNB 1described in the above embodiments may be provided by one or more radiostations (or RAN nodes).

The above-described embodiments have been described focusing on the cellreselection by the UE in the RRC_INACTIVE state. However, the networkslice availability may be configured, for example, not only for eachcell but also for each PLMN. That is, whether the desired network sliceof the UE 2 is available (or supported) in the camping cell may bedifferent between PLMNs. For example, the network slice availabilityinformation may be sent to the UE 2 per PLMN. When the desired networkslice is not available (or not supported) in the selected PLMN of the UE2, the UE AS layer may inform the NAS layer about it. At this time, theAS layer may also notify the NAS layer of the information regarding thenetwork slice per PLMN (e.g., information regarding whether the networkslice is available, or information regarding available network slices).Then, the NAS layer may execute PLMN selection in consideration of thisinformation received from the AS layer and may notify the AS layer aboutthe result (i.e., newly selected PLMN).

As already described, the above-described embodiments may be applied toother radio communication systems which support network slicing and usesthe RRC_INACTIVE state or a similar RRC state. For example, a case maybe considered in which LTE E-UTRAN (eNB) is connected to the 5G-CN andthe network slicing is supported in E-UTRAN cells. Furthermore, a casemay be assumed in which, as in the above-described RRC_INACTIVE state, astate (or a sub-state, or an operation mode) in which the UE and the eNBmaintain at least part of the AS context of the UE and the location ofthe UE is known to the E-UTRAN at a level of a predetermined areaconfigured by the E-UTRAN is supported. In this case, the predeterminedarea may be similar to the RAN notification area or may be the same asthe location registration area (e.g., TA) of the core network.

Further, the above-described embodiments are merely examples ofapplications of the technical ideas obtained by the inventors. Thesetechnical ideas are not limited to the above-described embodiments andvarious modifications may be made thereto.

For example, the whole or part of the above embodiments can be describedas, but not limited to, the following supplementary notes.

(Supplementary Note 1)

A base station placed in a Radio Access Network (RAN), the base stationcomprising:

a memory; and

at least one processor coupled to the memory and configured to controlstate transitions of a first radio terminal among first to third RRCstates, wherein

the first RRC state is a state in which the first radio terminal and theRAN maintain an access stratum (AS) context and in which a location ofthe first radio terminal is known to the RAN at cell level, the secondRRC state is a state in which the first radio terminal and the RANmaintain at least part of the AS context and in which the location ofthe first radio terminal is known to the RAN at RAN notification arealevel configured by the RAN,

the third RRC state is a state in which the first radio terminal and theRAN have released the AS context and in which the location of the firstradio terminal is not known to the RAN, and

the at least one processor is further configured to explicitly orimplicitly inform the first radio terminal about whether a first networkslice configured in the first radio terminal for data communication atleast in the first RRC state is available in each cell included in theRAN notification area.

(Supplementary Note 2)

The base station according to Supplementary Note 1, wherein the at leastone processor is configured to transmit, to the first radio terminal,first information explicitly indicating whether the first network sliceis available in each cell included in the RAN notification area.

(Supplementary Note 3)

The base station according to Supplementary Note 2, wherein the at leastone processor is configured to transmit the first information to thefirst radio terminal when configuring the RAN notification area in thefirst radio terminal.

(Supplementary Note 4)

The base station according to Supplementary Note 2 or 3, wherein the atleast one processor is configured to transmit the first information tothe first radio terminal during a procedure for moving the first radioterminal from the first RRC state to the second RRC state.

(Supplementary Note 5)

The base station according to Supplementary Note 1, wherein

the at least one processor is configured to include, in the RANnotification area for the first radio terminal, only one or more cellsin which the first network slice is available and configure the RANnotification area in the first radio terminal, and

the RAN notification area implicitly indicates that the first networkslice is available in each cell included in the RAN notification area.

(Supplementary Note 6)

The base station according to any one of Supplementary Notes 1 to 5,wherein the at least one processor is configured to receive from anotherbase station, through an inter-base station interface, informationindicating one or more network slices available or unavailable in eachcell of the other base station.

(Supplementary Note 7)

The base station according to any one of Supplementary Notes 1 to 6,wherein the at least one processor is configured to receive from asecond radio terminal, during a procedure for moving the second radioterminal from the second RRC state to the first RRC state or thereafter,second information indicating a second network slice which had beenconfigured in the second radio terminal when the second radio terminalwas formerly in the first RRC state.

(Supplementary Note 8)

The base station according to Supplementary Note 7, wherein the at leastone processor is configured to move the second radio terminal to anotherbase station or another cell when the second network slice is notavailable in the base station or in a cell to which the second radioterminal is connected.

(Supplementary Note 9)

The base station according to any one of Supplementary Notes 1 to 8,wherein

the first RRC state is an RRC_CONNECTED state,

the second RRC state is an RRC_INACTIVE state, and

the third RRC state is an RRC_IDLE state.

(Supplementary Note 10)

The base station according to any one of Supplementary Notes 1 to 9,wherein the RAN notification area is an area where, when the radioterminal in the second RRC state moves between cells by cellreselection, the radio terminal does not need to notify the RAN of thecell reselection.

(Supplementary Note 11)

A base station placed in a Radio Access Network (RAN), the base stationcomprising:

a memory; and

at least one processor coupled to the memory and configured to controlstate transitions of a radio terminal among first to third RRC states,wherein

the first RRC state is a state in which the radio terminal and the RANmaintain an access stratum (AS) context and in which a location of theradio terminal is known to the RAN at cell level,

the second RRC state is a state in which the radio terminal and the RANmaintain at least part of the AS context and in which the location ofthe radio terminal is known to the RAN at RAN notification area levelconfigured by the RAN,

the third RRC state is a state in which the radio terminal and the RANhave released the AS context and in which the location of the radioterminal is not known to the RAN, and

the at least one processor is further configured to transmit, in a firstcell of the base station, system information indicating one or morenetwork slices available or unavailable in the first cell.

(Supplementary Note 12)

The base station according to Supplementary Note 11, wherein the systeminformation is broadcast system information to be broadcast in the firstcell or is on-demand system information to be transmitted to the radioterminal in response to a request message from the radio terminal.

(Supplementary Note 13)

The base station according to Supplementary Note 11 or 12, wherein theat least one processor is configured to receive from the radio terminal,during a procedure for moving the radio terminal from the second RRCstate to the first RRC state or thereafter, information indicating afirst network slice which had been configured in the radio terminal whenthe radio terminal was formerly in the first RRC state.

(Supplementary Note 14)

The base station according to Supplementary Note 13, wherein the atleast one processor is configured to move the radio terminal to anotherbase station or another cell when the first network slice is notavailable in the base station or in a cell to which the radio terminalis connected.

(Supplementary Note 15)

The base station according to any one of Supplementary Notes 11 to 14,wherein

the first RRC state is an RRC_CONNECTED state,

the second RRC state is an RRC_INACTIVE state, and

the third RRC state is an RRC_IDLE state.

(Supplementary Note 16)

A radio terminal comprising:

a transceiver; and

at least one processor configured to control the transceiver in one ormore cells associated with a radio access network (RAN), wherein

the at least one processor is configured to control state transitions ofthe radio terminal among first to third RRC states,

the first RRC state is a state in which the radio terminal and the RANmaintain an access stratum (AS) context and in which a location of theradio terminal is known to the RAN at cell level,

the second RRC state is a state in which the radio terminal and the RANmaintain at least part of the AS context and in which the location ofthe radio terminal is known to the RAN at RAN notification area levelconfigured by the RAN,

the third RRC state is a state in which the radio terminal and the RANhave released the AS context and in which the location of the radioterminal is not known to the RAN, and

the at least one processor is further configured to check whether afirst network slice configured in the radio terminal for datacommunication at least in the first RRC state is available in a cell tobe reselected by cell reselection in the second RRC state.

(Supplementary Note 17)

The radio terminal according to Supplementary Note 16, wherein the atleast one processor is configured to receive, from a base station in theRAN, first information explicitly indicating whether the first networkslice is available in each cell included in the RAN notification area.

(Supplementary Note 18)

The radio terminal according to Supplementary Note 17, wherein the atleast one processor is configured to receive the first informationduring a procedure in which the first radio terminal transitions fromthe first RRC state to the second RRC state.

(Supplementary Note 19)

The radio terminal according to Supplementary Note 16, wherein

the RAN notification area includes only one or more cells in which thefirst network slice is available,

the at least one processor is configured to receive a configuration ofthe RAN notification area from a base station in the RAN, and

the at least one processor is configured to check whether the firstnetwork slice is available in the cell to be reselected, depending onwhether the cell to be reselected is included in the RAN notificationarea.

(Supplementary Note 20)

The radio terminal according to Supplementary Note 16, wherein

the at least one processor is configured to, in response to the cellreselection in the second RRC state, attempt to receive systeminformation indicating one or more network slices available orunavailable in the cell to be reselected,

the at least one processor is configured to, based on the systeminformation, check whether the first network slice is available in thecell to be reselected.

(Supplementary Note 21)

The radio terminal according to Supplementary Note 20, wherein thesystem information is broadcast system information to be broadcast inthe cell to be reselected or is on-demand system information to betransmitted to the radio terminal in response to a request message fromthe radio terminal.

(Supplementary Note 22)

The radio terminal according to any one of Supplementary Notes 16 to 21,wherein the at least one processor is configured to, in response tofailing to confirm that the first network slice is available in the cellto be reselected, transmit second information indicating the firstnetwork slice to a base station of the cell to be reselected, during aprocedure in which the radio terminal transitions from the second RRCstate to the first RRC state in the cell to be reselected or thereafter.

(Supplementary Note 23)

The radio terminal according to any one of Supplementary Notes 16 to 22,wherein

the first RRC state is an RRC_CONNECTED state,

the second RRC state is an RRC_INACTIVE state, and

the third RRC state is an RRC_IDLE state.

(Supplementary Note 24)

A method for a base station placed in a Radio Access Network (RAN), themethod comprising:

controlling state transitions of a first radio terminal among first tothird RRC states; and

explicitly or implicitly informing the first radio terminal aboutwhether a first network slice configured in the first radio terminal fordata communication at least in the first RRC state is available in eachcell included in a RAN notification area configured by the RAN, wherein

the first RRC state is a state in which the first radio terminal and theRAN maintain an access stratum (AS) context and in which a location ofthe first radio terminal is known to the RAN at cell level,

the second RRC state is a state in which the first radio terminal andthe RAN maintain at least part of the AS context and in which thelocation of the first radio terminal is known to the RAN at RANnotification area level,

the third RRC state is a state in which the first radio terminal and theRAN have released the AS context and in which the location of the firstradio terminal is not known to the RAN.

(Supplementary Note 25)

A method for a base station placed in a Radio Access Network (RAN), themethod comprising:

controlling state transitions of a radio terminal among first to thirdRRC states; and

transmitting, in a first cell of the base station, system informationindicating one or more network slices available or unavailable in thefirst cell, wherein

the first RRC state is a state in which the radio terminal and the RANmaintain an access stratum (AS) context and in which a location of theradio terminal is known to the RAN at cell level,

the second RRC state is a state in which the radio terminal and the RANmaintain at least part of the AS context and in which the location ofthe radio terminal is known to the RAN at RAN notification area levelconfigured by the RAN,

the third RRC state is a state in which the radio terminal and the RANhave released the AS context and in which the location of the radioterminal is not known to the RAN.

(Supplementary Note 26)

A method for a radio terminal, the method comprising:

controlling state transitions of the radio terminal among first to thirdRRC states; and

checking whether a first network slice configured in the radio terminalfor data communication at least in the first RRC state is available in acell to be reselected by cell reselection in the second RRC state,wherein

the first RRC state is a state in which the radio terminal and a radioaccess network (RAN) maintain an access stratum (AS) context and inwhich a location of the radio terminal is known to the RAN at celllevel,

the second RRC state is a state in which the radio terminal and the RANmaintain at least part of the AS context and in which the location ofthe radio terminal is known to the RAN at RAN notification area levelconfigured by the RAN,

the third RRC state is a state in which the radio terminal and the RANhave released the AS context and in which the location of the radioterminal is not known to the RAN.

(Supplementary Note 27)

A program for causing a computer to perform a method for a base stationplaced in a Radio Access Network (RAN), wherein the method comprises:

controlling state transitions of a first radio terminal among first tothird RRC states; and

explicitly or implicitly informing the first radio terminal aboutwhether a first network slice configured in the first radio terminal fordata communication at least in the first RRC state is available in eachcell included in a RAN notification area configured by the RAN, wherein

the first RRC state is a state in which the first radio terminal and theRAN maintain an access stratum (AS) context and in which a location ofthe first radio terminal is known to the RAN at cell level,

the second RRC state is a state in which the first radio terminal andthe RAN maintain at least part of the AS context and in which thelocation of the first radio terminal is known to the RAN at RANnotification area level,

the third RRC state is a state in which the first radio terminal and theRAN have released the AS context and in which the location of the firstradio terminal is not known to the RAN.

(Supplementary Note 28)

A program for causing a computer to perform a method for a base stationplaced in a Radio Access Network (RAN), wherein the method comprises:

controlling state transitions of a radio terminal among first to thirdRRC states; and

transmitting, in a first cell of the base station, system informationindicating one or more network slices available or unavailable in thefirst cell, wherein

the first RRC state is a state in which the radio terminal and the RANmaintain an access stratum (AS) context and in which a location of theradio terminal is known to the RAN at cell level,

the second RRC state is a state in which the radio terminal and the RANmaintain at least part of the AS context and in which the location ofthe radio terminal is known to the RAN at RAN notification area levelconfigured by the RAN,

the third RRC state is a state in which the radio terminal and the RANhave released the AS context and in which the location of the radioterminal is not known to the RAN.

(Supplementary Note 29)

A program for causing a computer to perform a method for a radioterminal, wherein the method comprises:

controlling state transitions of the radio terminal among first to thirdRRC states; and

checking whether a first network slice configured in the radio terminalfor data communication at least in the first RRC state is available in acell to be reselected by cell reselection in the second RRC state,wherein

the first RRC state is a state in which the radio terminal and a radioaccess network (RAN) maintain an access stratum (AS) context and inwhich a location of the radio terminal is known to the RAN at celllevel,

the second RRC state is a state in which the radio terminal and the RANmaintain at least part of the AS context and in which the location ofthe radio terminal is known to the RAN at RAN notification area levelconfigured by the RAN,

the third RRC state is a state in which the radio terminal and the RANhave released the AS context and in which the location of the radioterminal is not known to the RAN.

REFERENCE SIGNS LIST

-   1 gNodeB (gNB)-   2 User Equipment (UE)-   3 5G Radio Access Network (5G-RAN)-   4 5G Core Network (5G-CN)-   11 Cell-   1501 RF Transceiver-   1504 Processor-   1505 Memory-   1601 RF Transceiver-   1603 Baseband Processor-   1604 Application Processor-   1606 Memory

The invention claimed is:
 1. A gNB comprising: a controller configuredto communicate with a User Equipment (UE) in an RRC_CONNECTED statewhich uses a network slice, the controller configured to set cellinformation, the cell information defining one or more cells belongingto a RAN Notification Area, the cell information indicating only one ormore cells which support the network slice which the UE in theRRC_CONNECTED state uses while communicating with the gNB, the cellinformation being included in information related to the RANNotification Area in a Radio Resource Control (RRC) message to betransmitted from the gNB to the UE before the UE in the RRC_CONNECTEDstate is transitioned to an RRC_INACTIVE state; and a transmitterconfigured to transmit the RRC message to the UE in the RRC_CONNECTEDstate before the UE in the RRC_CONNECTED state transitions toRRC_INACTIVE state.
 2. The gNB according to claim 1, wherein theinformation related to the RAN Notification Area includes an identifierindicating an area of a RAN Notification.
 3. The gNB according to claim1, further comprising a receiver configured to receive a message fromanother gNB via a Xn interface, the message including network sliceinformation which indicates at least one network slice which issupported by at least one cell of the other gNB.
 4. The gNB according toclaim 1, further comprising a receiver configured to receive a messagefrom another gNB via a Xn interface, the message including a networkslice information which indicates at least one network slice which issupported by at least one cell of the other gNB, wherein the message istransmitted from the other gNB to notify the gNB of update of thenetwork slice information.
 5. A User Equipment (UE) which uses a networkslice, the UE comprising: a receiver configured to receive a RadioResource Control (RRC) message from a gNB to transition the UE in anRRC_CONNECTED state to an RRC_INACTIVE state, the RRC message includingcell information, the cell information defining one or more cellsbelonging to a RAN Notification Area, the cell information indicatingonly one or more cells which support the network slice which the UE inthe RRC_CONNECTED state uses while communicating with the gNB, the cellinformation being included in information related to the RANNotification Area in the RRC message, and a controller configured totransition the UE in the RRC_CONNECTED state to the RRC_INACTIVE state.6. The UE according to claim 5, wherein the information related to theRAN Notification Area includes an identifier indicating an area of a RANNotification.
 7. The UE according to claim 5, wherein the controller isfurther configured to decide whether the UE transmits a message toanother gNB based on whether information of a first cell on which the UEdecides to camp is included in the cell information.
 8. The UE accordingto claim 7, further comprising a transmitter configured to transmit themessage to the other gNB, if the information of the first cell on whichthe UE decides to camp is not included in the cell information.
 9. TheUE according to claim 7, further comprising a transmitter configured notto transmit the message to the other gNB, if the information of thefirst cell on which the UE decides to camp is included in the cellinformation.
 10. A method of a User Equipment (UE) which uses a networkslice, the method comprising: receiving a Radio Resource Control (RRC)message from a gNB to transition the UE in an RRC_CONNECTED state to anRRC_INACTIVE state, the RRC message including cell information, the cellinformation defining one or more cells belonging to a RAN NotificationArea, the cell information indicating only one or more cells whichsupport the network slice which the UE in the RRC_CONNECTED state useswhile communicating with the gNB, the cell information being included ininformation related to the RAN Notification Area in the RRC message, andtransitioning the UE in the RRC_CONNECTED state to the RRC_INACTIVEstate.
 11. The method according to claim 10, wherein the informationrelated to the RAN Notification Area includes an identifier indicatingan area of a RAN Notification.
 12. The method according to claim 10,further comprising deciding whether the UE transmits a message toanother gNB based on whether information of a first cell on which the UEdecides to camp is included in the cell information.
 13. The methodaccording to claim 12, further comprising transmitting the message tothe other gNB, if the information of the first cell on which the UEdecides to camp is not included in the cell information.
 14. The methodaccording to claim 12, further comprising transmitting the message tothe other gNB, if the information of the first cell on which the UEdecides to camp is included in the cell information.